1. Field of the Invention
This invention is in the field of separating and washing solid particles in suspension such as the separation of wort from insoluble grain residue.
2. DESCRIPTION OF THE PRIOR ART
Brewer's wort is usually produced by mixing finely ground, kiln dried malt with water in a masher, converting the starch into maltose and dextrins at temperatures of approximately 130.degree. to 167.degree. F., and clarifying the fermentable mash slurry by separating the liquid solids or spent grains. The separation of the wort from the isoluble grain residue in accordance with prior procedures has required three to four hours and may require in excess of five, depending on the quality of the malt being processed, on the type of clarifying or separating apparatus employed, and on the fineness of the ground malt.
The separation of brewer's wort from insoluble grain residue has historically been accomplished by using lautering tun or other type of stationary screening device. The mash is discharged into a lautering tun which is constructed with a perforated plate above the base. The mash is then allowed to settle for a length of time sufficient to establish a filter bed. The first wort withdrawn from the lautering tun is usually recycled until clear wort is obtained. The bulk of the first wort is run off and sparging is carried out as a separate operation.
The filtration characteristics of the mash are in part related to the fineness of the grind. A finely ground mash aids the biochemical conversion of the starch but reduces the filtration rate in the lauter tun. Coarse milling improves the filtration rate but hinders the starch conversion. It is accordingly necessary in practice to reach a compromise between good conversion and good filtration. In practice, in order to obtain high extract yields, it is considered necessary to add sparge water in excess of that needed to obtain a wort of the desired concentration in the brew kettle. The excess water must then be evaporated from the brew kettle.
Continuous lautering systems presently in use employ counter-current washing of the spent grain to obtain both a wort of the desired concentration in the brew kettle and spent grains with a low residual moisture content suitable for disposal. This is accomplished by using continuous screening centrifuges with internal washing. The problem in this type of installation is that fines pass through the screen with the wort making it necessary to clarify the wort prior to discharging it into the brew kettle. Another problem arises from the fact that the internal washes in the centrifuges are less efficient than dilution washes because the solution of the soluble extract is directly related to the time of treatment.
As examples of the patented prior art in this area, reference is made to the Henderson et al. U.S. Pat. No. 3,520,868 owned by the assignee of the present application. That patent describes a process for separating protein from soluble substances through the use of a solvent for the soluble portion. The steps involved in the process consist in introducing the protein-containing material into each of a series of succeeding zones along with a quantity of solvent from the next succeeding zone. The solvent and the dissolved material therein are then separated from the protein in each zone. The protein is passed onto the next succeeding zone for treatment. As the protein is withdrawn from the zone, the solvent containing the dissolved fats, sugars, starches and the like is also withdrawn from the zone and a portion of the withdrawn solvent is recycled back into the zone at the point of addition of the protein-containing material. The balance of the solvent is then passed back to the next preceding zones. Fresh solvent is introduced into the last zone in the series and the solvent withdrawn from the first zone is usually removed from the system for recovery, purification, or disposal.
The Harsanyi U.S. Pat. No. 3,535,116 describes a continuous method for the production of wort which includes the step of centrifuging the ground malt-water mixture continuously in a plurality of stages into a solid fraction and a liquid fraction, sparging the dehydrated solids fraction with water in controlled quantities at least in the last stage, removing the dehydrated solids, subjecting the liquid obtained by the centrifugal action to clarification, and delivering the clarified liquid to the brew kettle.